Investigation Of High Strength As-Cast Magesium Alloys

About 80% in total magnesium alloys are casting alloys, which are widely used in civil industry such as automobiles, 3C products as well as high-tech areas such as aerospace and military industry. Therefore to improve the strength of magnesium casting alloy is important both in theory and in engineering.Magnesium alloys with different compositions were fabricated by copper mold casting method. The as-cast samples with 3mm in diameter were checked by scanning electron microscopy and universal electronic material tester for the microstructures, fracture surfaces and mechanical properties. The main results are as following:Mg₉₀Cu₃Sn₇, Mg₉₀Cu₅Sn₅ and Mg₉₀Cu₇Sn₃ alloys were designed by considering gross alloying elements being 10%. Compared to other alloys, Mg₉₀Cu₃Sn₇ alloy presents the best mechanical properties characterized by the yield strength, the fracture strength and the plastic strain of 300MPa, 464MP and 11% respectively. While a high fracture strength of 550MP with moderate the yield strength of 300MPa and plastic strain of 9.7% was obtained for Mg₈₅Cu₅Sn₁Ca₄Y₅ alloy by using Ca and Y as strengthening elements. However, the fracture strength and plastic strain were reduced to 300MPa and 3.8% respectively for Mg₈₅Cu₅Sn₁Zn₅Ca₄ alloy when Y was replaced by Zn element. The mechanical properties for the alloys mentioned above give us suggestions that the Cu, as an alloying element, is not larger than 5% and the strengthening elements of Ca and Y, can increase the fracture strength, not the yield strength. Zn should be reduced in the investigated alloy.The best mechanical properties, i.e. fracture strength of 358MPa and plastic strain of 25%, for Mg-5%Sn-3%Nd alloy were observed among Mg-x%Sn-3%Nd (x=5, 6, 7) alloys, which indicates that the increase of Sn content deteriorates the properties. Therefore, it is concluded that the strengthening and toughening effect of Nd is superior to Sn by analysis the mechanical properties of Mg-5%Sn-7%Nd and Mg-7%Sn-5%Nd alloys through interchange of Sn and Nd elements. While the replacement of Y by Ca and Zn can deteriorate the mechanical properties either.Mg₈₀Zn(16-x)Ca₄Al_x(x=2, 4, 6) were designed by increasing alloying elements consideration. The fracture strengths, yield strengths and plastic strains are 560MPa, 310MPa and 5.3% respectively for x=2, 560MPa, 310MPa and 5.5% respectively for x=4 and 540MPa, 330MPa and 6.3% respectively for x=6. By further lowing Mg content, amorphous matrix was observed for Mg₇₅Zn₁₇Ca₄Al₄ alloy with yield strength of 600MPa, fracture strength of 635MPa and plastic strain of 1.2% respectively.